# 3 ways to divide polynomials

Polynomials can be divided just like numeric constants, either by factoring or by long division. The method you use will depend on how complex the dividend and divisor of the polynomial are.

## Steps

### Method 1 of 3: Determine Which Approach to Use

#### Step 1. Observe how complex the divisor is

The complexity of the divisor (the polynomial you will divide by) compared to the dividend (the polynomial you will divide by the divisor) will determine which is the best approximation.

• If the divisor is a monomial (a single-term polynomial), either a variable with a coefficient, or a constant (a number without a variable next to it), you can probably factor the dividend and cancel one of the resulting factors with the divider. See "Factoring the Dividend" for more instructions and examples.
• If the divisor is a binomial (two-term polynomial), perhaps you can factor the dividend and cancel one of the resulting factors with the divisor.
• If the divisor is a trinomial (three-term polynomial), you may be able to factor both the dividend and divisor, cancel the common factor, and then continue factoring the dividend or use long division.
• If the divisor is a polynomial with more than three factors, you will probably have to use long division. See "Using Division of Long Polynomials" for more instructions and examples.

#### Step 2. See how complex the dividend is

If by looking at the dividing polynomial you can't figure out whether you should try to factor the dividend, then look directly at the dividend.

• If the dividend has three terms or less, you can probably factor it out and cancel it with the divisor.
• If the dividend has more than three terms, you should probably divide it by the divisor using long division.

### Method 2 of 3: Factor the dividend

#### Step 1. Observe and try to find out if all the terms in the dividend contain a factor common to the divisor

If so, you can factor it and you can probably cancel it with the divisor.

• If you must divide the binomial 3x - 9 by 3, you can factor the 3 into both terms of the binomial, making it 3 (x - 3). Then you can cancel the divisor of 3, leaving a quotient of x - 3.
• If you must divide the binomial 24x3 - 18x2 times 6x, you can factor 6x into both terms of the binomial, turning it into 6x (4x2 - 3). You can cancel the divisor of 6x, leaving a quotient of 4x2 - 3.

#### Step 2. Look for special patterns in the dividend that tell you that you can factor it

Certain polynomials have terms that tell you that you can factor them. If one of those terms matches the divisor, you can cancel them, leaving the resulting factor as a quotient. Here are some patterns to look for:

• Difference of perfect squares. This is a binomial with the form ‘’ a2x2 - b '', where the values of '' a2’’ And ‘’ b2’’ Are perfect squares. These binomials can be factored into two binomials (ax + b) (ax - b), where a and b are the square roots of the coefficient and constants of the previous binomial.
• Perfect square trinomial. This trinomial has the form a2x2 + 2abx + b 2. It can be factored as (ax + b) (ax + b), which can also be expressed as (ax + b) 2. If the sign in front of the second term is a minus sign, the factors of the binomial will have the form (ax - b) (ax - b).
• Sum or difference of cubes. This is a binomial with the form a3x3 + b3 hear3x3 - b3, where the values from ‘’ to3’’ And ‘’ b3’’ Are perfect cubes. These binomials can be factored into a binomial and a trinomial. A sum of cubes is factored to (ax + b) (a2x2 - abx + b2). A difference of cubes is factored to (ax - b) (a2x2 + abx + b2).

#### Step 3. Use trial and error to factor the dividend

If you can't figure out a distinguishable pattern in the dividend to figure out how to factor it, you can try several possible factoring combinations. You can do this by first looking at the constant and trying to find several factors for it, and then the coefficient for the middle term.

• For example, if the dividend is x2 - 3x - 10, you could look at the factors of 10 and use 3 to determine which of the factor pairs is correct.
• The number 10 can be factored into factors of 1 and 10, or 2 and 5. Because the sign in front of it is negative, one of the binomials in the factorization must have a negative number in front of its constant.
• The number 3 is the difference between 2 and 5, therefore these must be the constants of the binomials of the factorization. Because the sign in front of 3 is negative, the binomial that 5 has must be the one with a negative sign. The factors of the binomial will therefore be (x - 5) (x + 2). If the divisor is one of these factors, you can cancel them, and the resulting factor will be the quotient.

### Method 3 of 3: Use long division of polynomials

#### Step 1. State the division

You should write long division of polynomials in the same way that you do to divide numbers. The dividend goes below the long division bar, while the divisor goes to the left.

• If you must divide x2 + 11 x + 10 times x +1, so x2 + 11 x + 10 goes under the bar, while x + 1 goes to the left.

#### Step 2. Divide the first term of the dividend by the first term of the divisor

The result of this division is written above the division bar.

• In our example, dividing x2, the first term of the dividend, times x, the first term of the divisor, gives x. You must write an x above the division bar, above the x2.

#### Step 3. Multiply the x in the quotient position by the divisor

Write the result of the multiplication under the leftmost terms of the dividend.

• Continuing with our example, multiplying x + 1 by x produces the result x2 + x. You should write this under the first two terms of the dividend.

#### Step 4. Subtract it from the dividend

To do this, first reverse the signs of the product of the multiplication. After subtracting, drag down the remaining terms of the dividend.

• By reversing the signs of x2 + x you will have –x2 - x. If you subtract this from the first two terms of the dividend, you will get 10x. After dragging down the remaining terms of the dividend, you will have 10x + 10 as a provisional quotient to continue with the division process.

#### Step 5. Repeat the previous three steps for the provisional quotient

Once again, you must divide the provisional quotient by the first term of the divisor, write that result above the division bar, after the first term of the quotient, multiply the result by the divisor, and then calculate what to subtract from it. to the provisional quotient.

• Since x goes 10 times in 10 x, you must write “+ 10” after x in the corresponding quotient position on the division bar.
• Multiplying x + 1 by 10 results in 10x + 10. You must write this below the provisional quotient and reverse the signs to do the subtraction, which will transform it into -10x - 10.
• When you do the subtraction, the remainder you will have will be 0. Therefore, divide x2 + 11 x + 10 times x +1 produces a quotient of x + 10. (You could have obtained the same result by factoring, but this example was chosen to make the division fairly simple.)